Preparation of sensitized lithographic plates, etc.



Patented July 13, 1943 2,324,197 T OFFlCE PREPARATION OF SENSITIZED LITE-l- GRAPHIC PLATES, ETC.

James P; Danehy, Cleveland Heights, Ohio, as-

signor to Harris-Seybold-Potter llornpany, Cleveland, ()hio, a corporation of Ohio No Drawing. Application July 2, 1941, Serial No. 400,793

20 (llairns.

The present invention relates to preparation of plates, suitably sensitized, for finishing up in order for printing such as in lithography; and more particularly there is inyolved novel sensitizable material and resultant plates, eliminating certain'drawbacks which have characterized the well-known albumin procedure.

Custo'marily, in preparing plates for lithographic printing, the plate, such as zinc or aluminum, is coated with an aqueous solution of albumin made sensitive to the action of light by addition of a sensitizing agent such as ammonium chromate or dichrornaten In the use of the plate, it is exposed to light in the form of the subject matter image which is to be printed, and they light hardens the albumin coating at exposed areas, then subsequently the developing ink is applied to the coating and on washing with wa r the uni'iardened areas are removed. A applying an etching solution to clean the non-image portio of the plate and render them receptive to We .fI'. the plate is emp 'ayed for printing. Although albumin is the E0: handing material-so used, there have been n well recognized objections to it. Albu- 1.111 is deficient in inherent water-repellency, and great skill is required to obtain proper results with it. carelessness may easily lead to loss of the image. Again, albumin coating solution deteriorates'rapio'ly, and usually there is considerable Waste due to spoilage; and furthermore the sensitivity of albumin coatings varies greatly in accordance with the elapsed time between coating and exposure and also with the relative humidity at the time of exposure, and particular care is necessary if successful results are obtained. Also, in the finished plate the half tone dots formed by albumin are of low mechanical strength and lack resistance to materials used in the dampening solution, and such dots decrease in size during printing, and small dots may be lost entirely. With the present invention, preparation of lithographic plates involving a widely-available material now becomes possible and with elimination of the disadvantages of the commonly-used albumin.

To the accomplishment of the foregoing and related ends, the invention, then, comprises the features hereinafter fully described, and particularly pointed out in the claims, the following description setting forth in detail certain illustrative embodiments of the invention, these being indicative however, of but a few of the various ways in which th principle of the invention may be employed.

The plate, suitably conditioned by removal of oxide. dirt, etc., as usual, and washed with water, is coated with a material, described more'in detail below, and sensitizing may be accomplished before or after the coating, preferably before, it

being an outstanding advantage that, unlike albumin, the material can be stocked in solution form, and also as a sensitized solution, thereby affording great convenience to operators.

For the coating or base material, I degrade a protein of casein type, as casein lrom milk, or the similarly-acting vegetable casein as in seeds such as soya bean, etc., and this degrading is performed by heating the casein or the like with an organic solvent or dispersing agent as it may more properly be called, as the protein is a colloid, and then removing the dispersing agent. As the inert organic liquid or dispersing agent I prefer ethylene glycol, or insome cases other glycol, as propylene glycol etc., and lessdesirably there may be employed such substances as glycerol, resorcinol, or other inert organic solvent of suitable boiling point to effect the desired change without combining with the protein. An illustration of the preparation of the degraded protein product, for instance, is to mix one part of casein with three or four parts of anhydrous ethylene glycol and heat the mixture with corn stant stirring, rapidly. Depending somewhat upon the size of the container and efiiciency the application of heat, there may be some variation in the length of time required toreach desirable maximum temperature. A satisfactory rate in general is to reach a, temperature of about 165 C. in about 94) minutes. A temperature of about 165 C, is generally sufficient as a manimum, and when this point has been reached the contents of the reaction vessel should be discharged or cooled. Desirably the reaction mixture is quickly cooled to about C., cooling being required only to an extent sufficient to avoid further degradation of the protein. Further cooling below 110 C. may be employed if desired but results in gelation which renders further processing difiicult. Then the degraded protein product is separated from the dispersing agent. Preferably this is accomplished by mixing the liquid mass with two or three times its volume, of a precipitating agent, i. e. an'agent which is miscible with the dispersing agent and is non-solvent for th proteinproduct, such as anhydrous acetone or less desirably ether, or the lower alcohols. By stirring, the solid degraded protein product is separated as a fine powder from the liquid phase containing the dispersing agent and precipitating agent. At this stage the product may be ground to a state of finer division, as in a ball mill, if desired. The product is then filtered, washed with more of the precipitating agent, and preferably vacuum dried. If desired, before subjecting the reaction mass to the precipitating agent, the solvent or glycol may 'be distilled off in part, and then the mixing with the precipitating agent may be carried out. The

product as dried is a light yellow powder. In the treatment, the initially high molecular weight protein is broken down into a simpler molecular structure whichis still proteinous. The solvent or dispersing agent being inert and neutral, the break-down is not of the drastic type involved in boiling with such hydrolytic agents as alkalies or acids, but water and ammonia are given 01!, and the product responds to general tests of protein, but differs from the initial protein in having new solubility characteristics and viscosity relations. It is soluble in 70-85 per cent aqueous alcohol, and in 70-85 per cent aqueous acetone. It is also soluble in water containing a small amount of an alkalin agent. Thus it is soluble in dilute ammonia, to the extent of about 95 per cent. Solution .occurs within a few hours, depending upon the concentration, and the solution may be put through a line filter or may be centrifuged to remove the insoluble portion. The concentration may vary, depending upon particular requirements. A convenient proportion with dilute alkalin solution is for instance 50 parts by weight of the powdered protein product to 435 parts or water and 15 parts of concentrated ammonia, 28 per cent. The solution may be stirred for about an hour and generally then it is desirable to allow it to stand quietly for three or four days or up to seven days, during which time the small insoluble portion which is thoroughly dispersed, separates out as a gray gelatinous precipitate which is removed by suitable means, for instance centrifuging. Such a clarifled solution has a concentration of about 9.5 per cent, specific gravity 1.03 and' viscosity 5-7 centipoises at 20 C. and a pH of about 9.5. If a dichromate solution as for sensitizing, be added to the ammonia water and powdered mixture shortly after it is made up, the dichromate may cause a precipitate. It is accordingly preferable to age the solution for about twenty-four hours, and then addition of dichromate does not tend to cause any precipitate. By making up initially rather high concentration solutions, further dilution to a desired extent may be provided by addition of water, as required. Generally, the minimum concentration satisfactory for application to plates is on the order of about 5 per cent. For sensitizing, a suitable sensitizing agent as known, may be applied, ammonium dichromate or chromate for instance, and illustrative amounts may be for instance one part of ammonium dichromate to three parts of the protein product. With the dichromate added, the pH of the solution for coating is about 7.0, whereas the pH of the initial clarified solution is around 9.5. The viscosity range as stated is rather critical. Below five centipoises the solutions as coated on plates yield images which are undesirably weak and above seven centipoises the solutions are so strong as to tend to cause trouble I in developing.

To prepare the plates in accordance with the invention, the plates, are counter-etched to remove oxide, dirt, etc. and are washed with water. And the plates are coated with the material and dried. If the sensitizer is incorporated in the protein solution, the plates are ready for exposing and finishing. Where the protein coating is applied without the sensitizer, the plates may be subsequently sensitized in a sensitizing solution, as for instance a water solution of ammonium dichromate.

While not necessary in all cases, I prefer, in preparing the plates, after counter-etching to remove dirt, oxide, etc., to "pre-etch or condition the surface by a solution containing a water-soluble natural gum, as for instance gum arabic, ghatti gum, tahla gum, etc., and one or more slightly acidifying salts such as the ammonium, potassium-or sodium salts of the common mineral acids, as nitric, phosphoric, hydrochloric, etc. Advantageously, asoiution of gum arabic, monoammonium phosphate and ammonium nitrate may be employed. For instance, desirable proportions are 600 cc. of a 14 Be. solution of gum arabic, and 22 grams of mono-ammonium phosphate and 22 grams of ammonium nitrate to 600 cc. of water. The pre-etching solution is brushed over the surface of the plate for a minute or somewhat more, and then the plate is washed with water; and while still damp a coating of degraded protein is applied and the plate may be whirled and dried. The pre-etch treatment prevents adsorption, having a special action with this coating, and particularly favoring the maintenance of printing contrast. The coated sensitized plate is exposed in usual manner, and may be developed by a developing ink and in water until the unexposed portion of the surface coating is removed.

It will be obvious to those skilled in the art that the coating herein described may be employed elsewhere in the graphic arts where a material adapted to form a light sensitive coating is required, for example, as a "cold-top enameP'in making plates by the photo-engraving process or as a "resist in making lithographic plates by the deep etch process.

This application is a continuation, in part and as to common subject matter of my application Ser. No. 297,776, filed October 3, 1939.

Other modes of applying the principle of the invention may be employed, change being made as regards the details described, provided the feain about 90 minutes and then being separated from the glycol.

2. A material adapted to form a light sensitive coating for use in preparing lithographic and other printing plates, which comprises a sensitized water-containing solution of the product of a protein of casein type heated with a glycol to degradation of the casein to about the extent as by bringing the temperature of the mixture up to about 165 C. 'inabout minutes and then being separated from the glycol. I

3. A material adapted to form a coating for use in preparing lithographic and other printing plates, which comprises a dilute ammonia solution of a degraded protein product of a casein type protein heated with an inert organ c dispersing agent to degradation of the protein to about the extent as by bringing the temperature of the mixture up to about C. in about 90 minutes and then being separated from the dispersing agent.

4. A material adapted to form, a coating for use in preparing lithographic and other printing plates, which comprises a solution in 70-85 Per cent aqueous alcohol of th degraded protein product of casein type heated with an inorganic dispersing agent to degradation of the protein to about the extent as by bringing the temperature of the mixture up to about 165 C. in about 90 minutes and then being separated from the dispersing agent.

5. A material adapted to form a coating for use in preparing lithographic and other printing plates, which comprises a solution in 70-85 per cent aqueous acetone f the degraded protein product of casein type heated with an inor anic dispersing agent to degradation of the protein to about the extent as by bringing the temperature of the mixture up to about 165 C. in about 90 minutes and then being separated from the dispersing agent.

6. A material adapted to form a coating for use in preparing lithographic and other printing plates, which comprises a solution in water, with a small amount of an alkaline agent, of th degraded protein product of a protein of casein type heated with an-inert organic dispersing agent to degradation of the protein to about the extent as by bringing the temperature of the mixture up to about 165 C. in about 90 minutes and then bein separated from the dispersing agent.

7. A material adapted to form a coating for use in preparing lithographic and other printing plates, which comprises the degraded protein product of casein heated with glycol todegradation of the casein to about the extent as by bringing the temperature of the mixture up to about 165 C. in about 90 minutes and then being separated from th glycol.

8. A material adapted to form a coating for use in preparing lithographic and other printing plates, which comprises the degraded protein product of casein heated with an inert organic dispersing agent to degradation of the casein to about the extent as by bringing the temperature of the mixture up to about 165 C. in about 90 minutes and then being separated from the dispersing agent.

9. A material adapted to form a coating for use in preparing lithographic and other printing plates, which comprises the degraded protein product of a protein of casein type heated with a glycol to degradation of the protein to about the extent as by bringing the temperatur of the mixture up to about 165 C. in about 90 minutes and then being separated from the glycol.

10. A material adapted to form a coating for use in preparing lithographic and other printing plates, which comprises the degraded protein product of a protein of casein type heated with an inert organic dispersing agent to degradation of the protein to about the extent as by bringing the temperature of the mixture up to about 165 C. in about 90 minutes and then being separated from the dispersing agent.

11. As a new article of manufacture, a plate for use in lithography or other printing having a surface comprising the degraded protein product of casein heated with a glycol to degradation of the casein to about the extent as by bringing the temperature of the mixture up to about 165 C. in about 90 minutes and then being separated from the glycol.

12. As a new article of manufacture, a plate for use in lithography or other printing having a surface comprising the degraded protein product of casein heated with an inert organic dispersing graded protein product agent to degradation of the casein to about the extent as by bringing the temperature of the mixture up to about 165 C. in about minutes and then being separated from the dispersing agent.

13. As a new article of manufacture, a plate for use in lithography or other printing having a surface comprising the degraded protein product of casein type heated with a glycol to degradation of the casein to about the extent as by bringing the temperature of the mixture up to about C. in about 90 minutes and then being separated from the glycol.

14. As a new article of manufacture, a plate for use in lithography or other printing having a surface comprising the degraded protein product of casein type heated with an inert organic dispersingagent to degradation of the protein to about the extent of bringing the temperature of the mixture up to about 165 C. in about 90 minutes and then being separated from the dispersing agent.

'15. As a new article of manufacture, a plate for use inlithography or other printing having a sensitized surface comprising the degraded protein product of a protein of casein type heated with a glycol to degradation of the casein to about the extent of bringing the temperature of the mixture up to about 165 C, in about 90 minutes and then being separated from the glycol.

16. As a new article of manufacture, a plate for use in lithography or other printing having a sensitized surface comprising the degraded protein product of a protein of casein type heated with an inert organic dispersing agent to degradation of the protein to about the extent as by bringing the temperature of the mixture up to about 165 C. in about 90 minutes and then being separated from the dispersing agent.

17. In preparing a plate for use in lithography or other printing, applying to the plate the degraded protein product of casein heated with a glycol to degradation of the casein to about the extent of bringing the temperature as by the mixture up to about 165 C. in about 90 minutes and then being separated from the glycol, and-subsequently treating the plate with a sensitizing solution.

18. In preparing a plate for use in lithography or other printing, applying to the plate the degraded protein product of casein type heated with a glycol to degradation of the protein to about the extent as by bringing the temperature of the mixture up to about 165 C. in about 90 minutes and then separating the glycol, and sub-'- sequently treating the plate with a sensitizing solution.

19. In preparing a plate for use in lithography or other printing, applying to the plate the degraded protein product of casein heated with a glycol to degradation of the protein to about the extent as by bringing the temperature of the mixture up to about 165 C. in about 90 minutes, then separating the glycol.

20. In preparing a plate for use in lithography or other printing, applying to the plate the deof casein type heated with a glycol to degradation of the protein to about the extent as by bringing the temperature of the mixture up to about 165 minutes, then separating the glycol.

JAMES P. DANEHY.

C- in about 90 

